Electric discharge tubes and circuits therefor



Aug. 5, 1958 G. H. HOUGH ET AL 2,846,611

ELECTRIC DISCHARGE TUBES AND CIRCUITS THEREFOR Filed Dec. 8, 1951 2 Sheets-Sheet 1 F/G./. F/G-.2

s a a K! Kl MP inventor G.H.H OUGH -T MJACKS ON Attorney 2,846,611 ELECTRIC DISCHARGE TUBES AND CIRCUITS THEREFOR Fiied Dec. 8, 1951 Aug. 5, 1958 s. H. HOUGH ETAL' 2 Sheets-Sheet 2 I'm PC IOOI/ I nventor -'-op v G H.HOUGHTM. JACKSON 5 G F a k U IP W H L m w m A [tome y United rates ldatent dice ELECTRIC DHSCHARQE TUBES AND CIRQIUTTS T HEREFGR George Hubert Hcugh and Thomas h ie' ion iaelsson, London, England, assignors to international Standard Electric Corporation, New York, N. Y.

Application December 8, 1951, Serial No. ZfillfidZ Claims priority, application Great Britain December 12, 195i) 3 Claims. (Q3. 313-496) This invention relates to cold cathode gas-filled electric discharge tubes and its object is to produce a tube capable of replacing a network of other electrical components acting as an electronic tool.

One feature of the invention comprises a cold cathode gas-filled electric discharge tube containing a plurality of substantially identical two-electrode gaps so constructed and arranged, and a gas mixture of such properties, that discharge across any one gap ionises all the other gaps, and that the potential required to discharge a gap so ionised and the potential required to maintain the discharge across a single gap are substantially the same.

A second feature of the invention comprises a cold cathode gas-filled electric discharge tube containing a plurality of substantially identical closely-spaced anode cathode gaps between a common electrode 01; one type and individual electrodes of the other type so constructed that individual gaps act as diodes and when suitably connected act as all electronic gates when the common electrode is used as an anode and act as one electronic gates when the common electrode is used as a cathode whereby an output pulse can be obtained when pulses are coincident on all diodes on the all case, and an output pulse can be obtained when a pulse occurs on any one of the diodes in the one case.

A third feature of the invention comprises a cold cathode gas-filled electric discharge tube containing a plurality of substantially identical anode-cathode gaps between a common electrode of one type and individual electrodes of the other type in which said gaps have a length of not more than about three millimetres and a spacing between any two individual electrodes of not more than about three millimetres and in which the gas pressure is of the order of 15-40 mihimetres of mercury whereby the striking and maintaining potentials of an 4 ionised gap are substantially the same, and the tube is adapted to constitute a diode network constituting an all or a one electronic gate.

The invention will be described with reference to the accompanying drawings in which:

Fig. 1 shows the construction of one form of gasdischarge tube incorporating the invention.

Fig. 2 shows a simple coincidence circuit using the tube of Fig. l.

3 shows an alternative more complex form of 5 tube in schematic manner while Fig. 4 shows a presently preferred form of tube of very simple construction.

Fig. 5 shows a coincidence tube of Fig. 4 type connected to a mixer tube consisting of a tube of the type shown in Fig. 3 in which the common electrode is used as cathode and its individual electrodes as anodes.

Fig. 6 shows rectifier networks performing the same functions as the coincidence tube and the mixer tube respectively.

The basic feature required for a tube to act as a coincidence circuit is that during operation, the striking and maintaining potentials of any gap forming part of the coincidence circuit proper shall be substantially the same. One gap must always be under discharge for coincidence circuit operation, and the property of multigap discharge tubes, that discharge in one gap ionises the gas in a closely adjacent gap, can therefore be utilised.

It has been discovered that the dominant constructional requirements of such a tube are that the spacing of the gaps should be as near as possible to the length of the cathode dark space of the gaps, and that the gas pressure shall be low.

The tube shown in Fig. 1 has an electrode structure in which one disc-like anode A provides a common electrode for a number of discharge gaps. The cathodes K of the gaps are 9 in number, 8 of which are spaced equally around the circumference of a circle and the ninth of which is at the centre of that circle. The working ends of all the cathodes K are in the same plane which plane is parallel to the plane of the anode A.

The central cathode is shown at K1 and. one of the outer ring cathodes is indicated at K2. The arrangement of the electrodes, the gas pressure and composition, are such that with any one of the gaps in a discharging condition any other of the gaps is coupled by ionisation coupling to the discharging gap. The whole electrode assembly is mounted on four mica plates such as M? which are themselves supported on supporting rods in well-known manner.

The actual measurements and other details of a tube which has proved satisfactory are as follows:

The assembly is mounted in an envelope which is filled with a mixture of neon and argon at a pressure of 25 mm. of mercury. Each of the cathodes is composed of 0.020" nickel wire and the 8 outer cathodes are on a pitch circle diameter of 3 mm. The perpendicular distance between the plane of the anode and that of the cathodes is also 3 mm.

Although these particular dimensions are given above, it should be appreciated that they are only provided by way of example. The general requirement, a has already been mentioned, is that a high degree of ionisation coupling should exist between any two gaps. In such circumstances the application to the tube of the +ve H. T. supply and earth potential to each of the cathodes tends to cause a glow discharge to spread equally over the cathodes, all cathode currents being equal, although manufacturing inequalities will usually result in the discharge concentrating on one or two gaps. This Will be ensured by making one of the cathodes more negative than the others e. g. -10 volts. However, the operation of the tube will be discussed on the basis that with the same cathode potentials, all the gaps will be discharging. When one of the cathodes is made more positive, say by applying a potential of +50 volts thereto, the glow discharge retreats from that gap. The reduction in current through that cathode is balanced by the sharing, by the remainder of the cathodes, of an equal current. Similar results are caused by other cathodes becoming positive and when the glow discharge is restricted to one gap by the remaining cathodes being positively biassed, then that one gap carries substantially the whole of the current through the tube. if this cathode is then given a positive potential the rise is transferred to the anode. Whether or not the discharge across a gap is extinguished completely when its cathode potential is raised depends particularly on the magnitude of that rise. The glow discharge may be caused to retreat from the gap and the cathode current may be very substantially reduced without actually extinguishing the gap completely. On the other hand if the rises in cathode potential are suflicient to cause extinction of discharge, then when the last gap is extinguished the anode potential will rise, mo-

mentarily at least to the full +H. T. supply voltage. This is not necessarily disadvantageous. If the potentials on the cathodes were raised by different ambients, an output pulse would be obtained on the anode equal to'the min 'imum potential rise on any cathode.

- One method of operation of such a tube will now be described with reference to Fig. 2. In Fig. 2 the cathodes are shown, for the sake of convenience, in plan view whilst the anode is shown in elevation. The legend beside each cathode represents the designation of the gap between'that .cathode and the anode, e. g. G1. It must be remembered that all the gaps are of equal length.

In operation the tube normally has the glow discharge confined to gap G1. This is because at the terminal P1 a lower potential, 10 v., is applied than the zero potential on theother cathodes which causes the potential difference across that gap to be greater than across the other gaps so that the discharge concentrates in that one gap. With gap G1 discharging, all the other gaps will be ionised, and the potential across them will be adequate for striking'the other gaps. At the point P1 positive-going pulses are applied'at a predetermined frequency and these will be referred to as the control pulses. When the next control pulse matures at P1 the glow discharge of gap -G1 is caused to retreat, and because all gaps are coupled by ionisation coupling, one or more of the other gaps are fired automatically. At the trailing edge of the control pulse the glow discharge returns again to gap G1 because the normal potential level at the terminal P1 is lower than on any other of the terminals. On the resumption of substantial current flow through gap G1 the other gaps cease to carry appreciable current.

The operation will now be considered with positive potentials applied to all the terminals P1 to P9 possibly in different time cycles and possibly with different pulse durations. With such pulse cycles, there is always a recurrent time position pulse when all the pulses are coincident, and which has a long recurrence time compared with'the individual pulse time cycles. When this coincidence time occurs, the positive pulse potentials applied to the outer ring cathodes prevent any of their'gaps firing so that the rise of potential on the cathode of P1 is trans ferred to the anode. Hence for the duration of pulse coincidence an output pulse is obtained at the output terrninal OT. It will be appreciated that only when all the cathodes are simultaneouslyat a positive potential is this output pulse obtained. Hence a tube of the construction described operating on the principle that has been set forth above, provides a coincidence gating circuit.

Fig. 3 shows a tube in which the problem of obtaining adequate inter-ionisation of the gaps has been eased by providing priming gaps. In this construction each main gap has its own priming gap and is screened from adjacent gaps. The main gaps G18 each with its own priming gap P18 are arrangedas in Fig. l in a circle and are screened from adjacent gaps by radial screens RS.

Alternatively, the centre gap of Fig. 1 could be used solely as a priming gap, thus reducing the effective gap provision in the tube from nine to eight as in Fig. 3.

The problem of bringing the gaps close together is more satisfactorily solved in the construction of Fig. 4 in which the cathodes are L-shaped, the long legs being mounted in a circle in the usual mica plates with the shorter legs pointing radially inwards towards the centre of the circle so that the adjacent ends of the cathodes are on a circle of 1 mm. diameter. The vertical distance between the disc anode A and each cathode is 2 mm. The gaps are fully ionised at the extremities of the cathodes, one from another. The gaps strike from the cathode extremity t the anode, but the discharge spreads'along the leg of the cathode which is parallel to the anode. No priming gaps or screens are used. In this tube the gas pressure may be of the order of 25 millimetres of mercury, the gas as before being a neon-argon mixture. 7

Such a tube with four gaps has an initial unprlmed striking voltage of 125 v., a primed or ionised striking voitag'e of slightly over 110 v. but less than 111 v., and a maintaining voltage of 110 v. l

The effective impedance of a conducting gap is about 10,000 ohms and of a non-conducting gap hundreds of megohms. The variation in maintaining voltage of a gap due to a change of 40 v. in the potential across a neighbouring non-conducting gap is only 0.2 v. The current range of the tube is between 50 and 300 microamperes.

In this tube, a certain time is required for the current to change from one cathode to an adjacent cathode when the potential conditions of the gaps causes a transfer of the discharge from one gap to another. This produces a small change in anode voltage-lasting for a few microsecondswhen a fast pulse is applied to a gate which is closed; that is when one or more cathodes are at zero potential, and no output can be obtained. When the gate is open, however, that is, when the potential on all other cathodes has been raised; the application of a fast pulse on the control cathode actually extinguishes the discharge, and in this case the anode voltage overshoots (positively) the maintain value. The result is an increase in the voltage pulse appearing at the anode, and in some circumstances the tube may actually give a gain.

Such tubes may be .used with the common electrode as anode and the individual electrodes as cathodes as previously described. Alternatively the same tube may be used with the common electrode as cathode and the individual electrodes as anodes. The only difference in the two cases will be in the finish of the electrodes for whichever purpose they are to be used. The finishes or coatings will be of normal type In use such as common cathode tube D2, Fig. 5, will act as a mixer valve, a change of potential on any one anode giving an output pulse on the cathode. Asshown the cathode is connected via a cathode resistance of the order of two megohms to say 100 v., while the anodes are individually connectedvia anode resistances of the order of one megohm to +300 v. and to individual inputs from tubes D1 such as shown in Fig. 2.

Normally the anode potentials of tube D2 are the same, but if one anode potential rises then a positive potential movement appears across the cathode load,

and the other anodes are effectively decoupled. The tube D2 is of the type shown in Fig. 3 but isshown with all the individual electrodes in line.

As the tube is acting as a mixer tube the individual electrodes are anodes and the common electrode is the cathode. Each main gap formed by an anode A has its own priming gap formed by a priming anode PA. Each pair of anodes A, PA is screened from adjacent pairs by a screen S at v. The priming anodes are connected via individual resistances of 5 megohms to +300 v.

Fig. 5 shows one type of tube acting as coincidence tube connected to another type of tube acting as mixer tube. The roles could be exchanged, or both tubes could be of the same type.

Operation of the coincidence tube D1 is improved by employing one of the cathodes PC solely to maintain 'a small auxiliary discharge. The function of this discharge is to prime the other gaps and thus to reduce the difference between breakdown and sustain. The cathode PC is connected via a resistance of 5 megohms to v., while the anode is connected via 1 megohm to +300 v.

The priming gap doesnot affect the operation of the coincidence gaps and as before when the potential on all the cathodes are raised, an output pulse is obtained.

The output D1 is connected to an anode of D2 and other anodes are connected each to the output of a corresponding tube D1. In the normal condition a current will be flowing from one or more of the anodes via the common cathode resistance to -100 volts. The voltage at the output terminal will be less, by the maintaining voltage of D2, than the voltage of the most positive anode. Thus if the potential of any anode is varied there will be a corresponding variation at the cathode, if that particular anode is more positive than any other. Anodes which are less positive will be automatically disconnected from anodes and from the common cathode. Therefore when the anode 1 moves positively under conditions of coincidence of positive voltage on inputs it to 6, then a positive movement appears across the cathode lead of D2, the other anodes of D2 being elfectively decoupled.

It will be seen that the coincidence tube and the mixer tube are the electrical equivalent respectively of the lefthand and right-hand dry plate rectifier gates of Fig. 6. Each rectifier is the equivalent of a gas diode consisting of an individual electrode and the respective portion of the common anode. Coincident circuits are commonly known as all gates, since pulse coincidence on all diodes is necessary for generation of an output pulse, whereas mixer circuits are commonly known as one gate since a pulse on any one of them gives rise to an outgoing pulse.

The gas tube diodes have much smaller forward resistance and much larger backward resistance than dry plate rectifiers and do not suifer from capacity effects.

While the principles of the invention have been described above in connection with specific embodiments and particular modifications thereof, it is to be clearly understood that this description is made by way of example aud not as a limitation on the scope of the invention.

What We claim is:

1. A cold cathode gas-filled electric discharge tube comprising, an envelope, a gaseous atmosphere in said envelope, a plurality of electrodes defining a plurality of diode gaps, means for positioning the electrodes defining separate gaps adjacent each other so that the firing of one gap ionizes all the other gaps, and means for positioning the two electrodes of each gap within a distance of each other so near the length of the cathode dark space in said gaseous atmosphere that upon such ionization the striking and maintaining potentials for each gap are substantially the same.

2. A cold-cathode gas discharge tube as claimed in claim 1 in which said gaps have a length of not more than three millimetres, in which the distance between any two individual electrodes is not more than three millimetres and in which the gas pressure is between 15-40 millimetres of mercury.

3. A cold cathode gas discharge tube as claimed in claim 2 in which the individual electrodes are arranged in a circle having a diameter of the order of one millimetre.

4. A cold cathode gas discharge tube as claimed in claim 3 in Which the individual electrodes are L-shaped, the operative legs being parallel to the common electrode, being radial with their free ends forming a circle having a diameter of the order of 1 millimetre, and in which the gas pressure is 1540 millimeters of mercury.

5. A cold cathode gas discharge tube as claimed in claim 1 in Which priming gaps are provided for facilitating ionisation of the diode gaps.

6. A cold cathode gas discharge tube as claimed in claim 1 in which a priming gap is provided for each diode gap and in which the pairs of diode and priming gaps are screened from one another.

7. A cold cathode gas-filled discharge tube as claimed in claim 1 in which the gas is a neon-argon mixture having a pressure of 15-40 millimetres of mercury.

8. A cold cathode gas-filled electric discharge tube containing a plurality of substantially identical two electrode diode gaps all positioned adjacent each other so that discharge across any one gap ionizes all the other gaps, the gas atmosphere being of low pressure and the length of the gaps being near the length of the cathode dark space so that the potential required to discharge a gap so ionized and the potential required to maintain the discharge across a single gap are substantially the same, a priming gap for each diode gap, and means screening the pairs of diode and priming gaps from one another.

References Cited in the file of this patent UNITED STATES PATENTS 2,402,019 Carpenter June 11, 1946 2,565,103 Toulon Aug. 21, 1951 2,575,370 Townsend Nov. 20, 1951 2,575,517 Hagen Nov. 20, 1951 2,579,306 Depew et al Dec. 18, 1951 2,618,767 VOn Gugelberg Nov. 18, 1952 OTHER REFERENCES Gaseous Conductors, by I. D. Cobine, Phop. 13, page 517. Publ. by McGraw-Hill Book Co., New York, N. Y.. 1941. 

